Collision rates for excitation of helium-like ions with inclusion of resonance effects

Abstract

Collisional excitation rate coefficients are given for all 21 fine-structure transitions involving the ground level and/or singly excited n = 2 levels in 18 He-like ions with nuclear charge number Z between 8 and 74. The calculations are done in intermediate coupling, including the contributions from all resonances associated with certain autoionizing levels of Li-like ions. The resonance contribution is obtained by calculating directly the rates for certain processes, including the effect of radiative decay of the autoionizing levels. Resonance enhancements by more than a factor of two are found for some of the spin change transitions between the n = 2 levels. The results are compared with those obtained by other authors.